Help with Slug-VOF

MIJAIL

Hi everybody, I'm trying to simulate a two-phase slug flow (water and air) in a horizontal pipe (0.078m x 36m) until now I can't make it work, i don't know how to especify superficial velocities in FLuent for both phases, so I tried first (because of the large relation diameter-lenght of the pipe) making a pipe of 1m leght and make a periodic arrengement, and then specifying the pressure gradient, it didn't work. I don't know how to express the separation between phases, or specify the inicial volume fraction (wich is known), velocities (wich are diferent for each phase in this case, and known also), so any ideas??? Thank you very much in advance.